History of the Synthesizer (by Yamaha): https://hub.yamaha.com/keyboards/synthesizers/history-of-the-synthesizer-part-1/
https://hub.yamaha.com/keyboards/synthesizers/history-of-the-synthesizer-part-2/

Synthesizers:
https://dotpiano.com/
https://aikelab.net/websynthv2/  (easy to use)
https://www.gsn-lib.org/apps/cardboardsynth/index.html
https://waveform.playtronica.com
https://juno-106.js.org/
https://midi.city/
https://sodaphonic.com/instruments/synth
https://learningsynths.ableton.com/ (very cool and good for younger students)
https://www.femurdesign.com/theremin/ (simple)

List of many web synths (some above found here): https://synth.playtronica.com/

Sequencers:
https://artsexperiments.withgoogle.com/ar-synth/
https://soundation.com/

Loopers/Drum Machines/Virtual Kit:
https://www.onemotion.com/drum-machine/
https://patternsketch.com/
https://drumbit.app/
https://www.tony-b.org/
https://www.virtualdrumming.com/drums/online-virtual-games/hip-hop-drum-kits.html
https://roland50.studio/
https://sb.bitsnbites.eu/
https://errozero.co.uk/acid-machine/

Fun:
https://apps.musedlab.org/soundbreaking/toc/ (Tech Tools)
https://apps.musedlab.org/variation-playground/paths/puck/
https://apps.musedlab.org/variation-playground/paths/sibelius/
https://apps.musedlab.org/aqwertyon/theory/C-4-major
https://apps.musedlab.org/variation-playground/layers/dvorak/
https://youdj.online/
https://isleoftune.com/

WebSynths (Groove maker & Synth):
https://www.websynths.com/

Making Music (easier):
https://touchpianist.com/
https://musiclab.chromeexperiments.com/
https://synth.playtronica.com/groove-pizza/
https://www.mod-synth.io/
https://musiclab.chromeexperiments.com/